The isolation and chemical characterization of the ACTH receptor(s) from beef adrenal cortex is the prime goal of this investigation. C14- labeled biologically active fragments of ACTH will be used to detect ACTH receptors in sub-cellular organelles of beef adrenal homogenates. Particulate fractions which exhibit a high binding capacity for ACTH will be produced in sufficient amounts for isolation experiments. Such fractions will also serve to study the relation between binding and peptide structure. A number of ACTH analogs and fragments are available from previous work relating structure and in vivo steroidogenic activity. Others will be synthesized as needed. These studies are designed to delineate "attachment" and "binding" sites in ACTH and will guide efforts toward development of competitive ACTH antagonists. The ability of the ACTH fragments and analogs to activate the adenyl cyclase complex in particulate fractions from beef adrenal cortex will be correlated with their ability to bind.